Schedule I - Condensed Financial Information of Registrant - Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating Activities
Net cash provided by operating activities	$ 626.1	$ 534.3	$ 449.2
Investing Activities
Purchases of leased-in assets	(117.1)	(118.4)	(150.5)
Proceeds from sale-leasebacks	82.5	0.0	0.0
Portfolio proceeds and other	223.7	482.2	264.0
Net cash used in investing activities	(394.9)	(307.6)	(878.5)
Financing Activities
Repayments of debt (original maturities longer than 90 days)	(800.0)	(726.3)	(819.8)
Net increase (decrease) in debt with original maturities of 90 days or less	(3.6)	(64.5)	50.0
Proceeds from issuances of debt (original maturities longer than 90 days)	859.4	748.8	1,223.0
Stock repurchases	(120.1)	(125.4)	(124.6)
Dividends	(67.4)	(68.2)	(62.0)
Other	10.4	9.3	(1.8)
Net cash (used in) provided by financing activities	(124.9)	(229.0)	262.2
Net (decrease) increase in cash and cash equivalents during the period	105.1	(7.5)	(169.8)
Cash and Cash Equivalents at beginning of period	202.4	209.9	379.7
Cash and Cash Equivalents at end of period	307.5	202.4	209.9
Parent Company [Member]
Operating Activities
Net cash provided by operating activities	632.8	412.5	219.5
Investing Activities
Capital additions	472.7	602.9	748.1
Purchases of leased-in assets	(108.4)	(118.4)	(150.5)
Proceeds from sale-leasebacks	82.5	0.0	0.0
Portfolio proceeds and other	127.8	208.7	169.5
Net cash used in investing activities	(370.8)	(512.6)	(729.1)
Financing Activities
Repayments of debt (original maturities longer than 90 days)	(661.0)	(350.0)	(692.2)
Net increase (decrease) in debt with original maturities of 90 days or less	0.0	(69.0)	69.0
Proceeds from issuances of debt (original maturities longer than 90 days)	677.6	695.7	1,188.7
Stock repurchases	(120.1)	(125.4)	(124.6)
Dividends	(67.4)	(68.2)	(62.0)
Other	10.4	2.3	(1.6)
Net cash (used in) provided by financing activities	(160.5)	85.4	377.3
Net (decrease) increase in cash and cash equivalents during the period	101.5	(14.7)	(132.3)
Cash and Cash Equivalents at beginning of period	147.6	162.3	294.6
Cash and Cash Equivalents at end of period	$ 249.1	$ 147.6	$ 162.3

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Purchases of leased-in assets.

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